connector-gmail: detect Outlook reply header as quoted content

[KrisBraun]

Summary

• The HTML quote-stripping only matched Gmail's gmail_quote class and Outlook web's appendonsend/divRplyFwdMsg ids. Microsoft Outlook desktop and corporate Exchange clients (e.g. Gowlings) wrap replies with a bolded From: / Sent: / To: / Subject: header block inside a <div style="border-top:..."> divider (or <hr>), so the whole prior thread got re-ingested into every note.
• Detect the bolded four-header sequence in close proximity, then walk back up to 1000 chars to cut at the nearest <hr> or border-top <div>; if neither is present, cut at the start of the wrapping <p>/<div>. Requiring all four headers (not three) keeps ordinary prose from triggering the matcher.

Test plan

• Sanity-checked against synthetic samples covering: Outlook desktop (border-top div), OWA (hr divider), no-divider, <strong> instead of <b>, no-quote (unchanged), and gmail_quote precedence — all pass.
• pnpm build clean in connectors/gmail.
• After deploy, verify a fresh Gowlings reply in the original thread comes in with quoted content stripped.

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